1. Field of the Invention
The present invention relates to a novel fluoroorganopolysiloxane and a process for preparing the same.
2. Description of the Prior art
Organopolysiloxanes have low surface tension and low refractive indexes, and are excellent in properties such as heat resistance, cold resistance, electrical insulation properties, water repellency, release properties, defoaming properties and chemical resistance; hence they are nowadays used in extensive industries. However, the recent progress of technology requires development of organopolysiloxanes excellent in various properties capable of satisfying high level of requirements. In attempt to satisfying the requirements, for example, organopolysiloxanes having a fluorine-containing organic group were proposed, and several process for preparing them were proposed (Japanese pre-examination patent publication Nos. 47605/1987, 47608/1987, 49305/1987, 529/1988, 27530/1988, and 41530/1988).
In preparing heat-vulcanization type silicone rubber compounds, an organopolysiloxane having a large polymerization degree with a viscosity of 1.times.10.sup.6 cP or more is essential as a main ingredient, because an organopolysiloxane with a lower polymerization degree is liable to adhere to rolls when worked with a roll mill and worsen workability extremely, and because resulting compounds produce only cured products with poor mechanical properties such as strength and elongation. Fluorosilicone rubbers have good heat resistance, oil resistance, release properties, etc., and require a fluorine-containing organopolysiloxane with a large polymerization degree as a raw material. The present invention provides a novel fluoroorganopolysiloxane containing a perfluoroalkylether group and having a sufficiently large polymerization degree, which can be used as a raw material as described above.
As a process of preparing such a high molecular weight fluoroorganopolysiloxane containing a perfluoroalkylether group, a process may be proposed in which a cyclotrisiloxane having the perfluoroalkylether group is synthesized, and then polymerized according to a known process, i.e., it is polymerized in the presence of such a catalyst as silanolates of alkali, e.g., Li, Na, K and Cs at 100.degree. to 180.degree. C. It has been found, however, that according to this process, depolymerization also occur, thereby producing a polymer containing a considerable amount of low molecular weight compounds; hence it is impossible to produce the desired polymer with a large polymerization degree in a good yield.